Do you have backups?
If so, what kind?
If not, you've learned a lesson the hard way (as most of us did ). But you've lost much less than many others; take the opportunity to start doing regular backups before something worse happens.
You already have Time Machine on your Mac. You might want to review the Time Machine Tutorial, and perhaps browse Time Machine - Frequently Asked Questions. If you don't like Time Machine, #27 in the FAQ article has some alternatives.